This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The first goal is to continue investigating the structural basis of the extramembraneous domains of K channels from eukaryotes and prokaryotes. Our recent work of cytoplasmic regulatory domain of inwardly rectifying K channels will be further expanded complexes containing its cytoplasmic regulatory proteins such as PDZ-binding domain of membrane anchoring proteins and small-molecule ligands such as PIP2. Crystals of several mutants have been generated to delineate the significance of conformational flexibility in association with channel gating (Pegan et al., 2005). The second goal is to obtain the high-resolution structure of Mistic and Mistic variants in the absence or presence of different detergents. One such variant of Mistic we named M2 has been crystallized and shows diffraction to ~3.2 Angstrom. The protein will be complexed by its cargo proteins. Systematic analyses of these related structures will help understanding the action mechanism of Mistic in assisting protein integration into hydrophobic membrane.